Hydroprocessing is a commonly used technique in a refinery for improving the characteristics of a feedstock. Depending on the nature of the feed and the desired product, hydroprocessing can be used to remove contaminants such as a sulfur or nitrogen; modify the boiling range of a feed to form higher value products; modify the properties of a feed, such as cold flow properties or viscosity properties; or saturate olefins in aromatics in the feed.
One goal in selecting hydroprocessing reaction is to select reaction conditions that avoid undesirable side reactions. Unfortunately, the nature of some types of feeds makes it difficult to completely avoid such side reactions. For example, feedstocks corresponding to vacuum resid fractions are a potentially desirable feedstock for hydroprocessing. Heavy oil feed such as vacuum resids often contain substantial quantities of heteroatoms, so hydroprocessing can be valuable for removal of contaminants. Due to the relatively high boiling range of a vacuum resid feed, converting portions of the feed to lower boiling fractions can also be desirable. However, vacuum resid feeds are difficult to process in conventional fixed bed hydroprocessing reactors. This is due in part to the tendency of such feeds to cause coke formation on catalyst that is exposed to the feed. This coke formation can eventually lead to “plugging” within the catalyst bed. As used herein, plugging refers to any type of change or degradation in the flow characteristics of a catalyst bed due to coke formation. As coke formation increases the amount of coke present in the bed, the required pressure to pass a feed through the catalyst bed can increase. A sufficient amount of coking can eventually cause the catalyst bed to become unsuitable for further hydroprocessing. At this point, the hydroprocessing reactor has to be shut down to allow for replacement of the catalyst in the catalyst bed.
For reaction systems where plugging can occur due to coke formation, there is a need to mitigate the effects of plugging. Allowing a reactor to continue running until plugging occurs can allow for an increased run time in the short term, but having to shut the reactor down to exchange catalyst is usually a lengthy procedure. Methods for exchanging catalyst during operation can also be used, but such systems usually require an internal reactor structure different from a fixed bed, and thus can pose other challenges.
U.S. Pat. No. 8,380,435 describes methods for windowed statistical analysis for anomaly detection in geophysical datasets. Various statistical methods are used to identify geophysical features and characteristics based on seismic data and/or other types of data. The geophysical features can then be used to identify, for example, likely locations for hydrocarbon deposits.